Present wire-feed welders in industry rely on motor feed rates to control output current by controlling the burn rate of the wire. The faster the motor feeds the wire, the higher the output current. Generally, where current is controlled by motor feed, the voltage may drop as the current need rises. As the user gains greater experience with the equipment, the user may adjust both the input voltage and the motor feed rate to achieve a proper weld. Sometimes, however, the experience is gained by ruining either the welded material or the weld.
In a welder, an electromechanical switch known as a contactor, is used to feed power source current through the electrode. Because the electromechanical switch relies upon moving contacts to turn the current ON and OFF, arcing at electrical contacts within the contactor in the power source. Thus, operation leads to degradation of performance. The degradation of performance is exhibited in an increased contact resistance that causes an equal decrease in output voltage and current. With continued use, these devices will self-destruct by overheating and eventually fail. During the period leading up to the total failure of the power source, the power provided at the welding arc will produce degraded welds. The nature of the degraded welds will require extensive and expensive rework of those welds.
What is needed is a solid-state power supply for wire feed welding in constant current and constant voltage modes that will neither arc nor degrade in performance during operation.